Drugs, including the anticonvulsant phenytoin, some antibiotics (such as chloramphenicol, nitrofurantoin, and sulfonamides), some chemotherapy drugs (such as vinblastine and vincristine), and some sedatives (such as barbital and hexobarbital)

Cancer (such as multiple myeloma), which damages nerves by directly invading or putting pressure on them or by triggering an autoimmune reaction

The most common form of chronic polyneuropathy usually results from poor control of blood sugar levels in people with diabetes but may result from excessive use of alcohol.

Diabetic neuropathy refers to the several forms of polyneuropathy that diabetes can cause. (Diabetes can also cause mononeuropathy or multiple mononeuropathy, which leads to weakness, typically of the eye or thigh muscles.)

Symptoms of Polyneuropathy

Acute polyneuropathy (as occurs in Guillain-Barré syndrome) begins suddenly in both legs and progresses rapidly upward to the arms. Symptoms include weakness and a pins-and-needles sensation or loss of sensation. The muscles that control breathing may be affected, resulting in respiratory failure.

In the most common form of chronic polyneuropathy, only sensation is affected. Usually, the feet are affected first, but sometimes the hands are. A pins-and-needles sensation, numbness, burning pain, and loss of vibration sense and position sense (knowing where the arms and legs are) are prominent symptoms. Because position sense is lost, walking and even standing become unsteady. Consequently, muscles may not be used. Eventually, they may weaken and waste away. Then, muscles may become stiff and permanently shortened (called contractures).

Diabetic neuropathy commonly causes painful tingling or burning sensations in the hands and feet—a condition called distal polyneuropathy. Pain is often worse at night and may be aggravated by touch or by a change in temperature. People may lose the senses of temperature and pain, so they often burn themselves and may have open sores caused by prolonged pressure or other injuries. Without pain as a warning of too much stress, joints are susceptible to injuries. This type of joint injury is called neurogenic arthropathy (Charcot joints).

Polyneuropathy often affects the nerves of the autonomic nervous system, which controls involuntary functions in the body (such as blood pressure, heart rate, digestion, salivation, and urination). Typical symptoms are constipation, sexual dysfunction, and fluctuating blood pressure—most notably a sudden fall in blood pressure when a person stands up (orthostatic hypotension). The skin may become pale and dry, and sweating may be reduced. Much less often, control of bowel movements or urination is lost, leading to fecal or urinary incontinence.

People who have a hereditary form may have hammer toes, high arches, and a curved spine (scoliosis). Abnormalities in sensation and muscle weakness may be mild. Affected people with mild symptoms may not notice the symptoms or may consider them unimportant. Other people are severely affected.

How completely people recover depends on the cause of polyneuropathy.

Diagnosis of Polyneuropathy

A doctor's evaluation

Electromyography and nerve conduction studies

Blood and urine tests to determine the cause

Doctors usually recognize polyneuropathy by the symptoms. A physical examination can help doctors diagnose polyneuropathy and identify the cause. Electromyography and nerve conduction studies are usually done, particularly in the legs and feet. These tests may be used to do the following:

Determine what type of damage is causing the problem—for example, whether the myelin sheath around nerves is damaged (called demyelination)

After polyneuropathy is diagnosed, its cause, which may be treatable, must be identified. Doctors ask whether other symptoms are present and how quickly the symptoms developed. This information suggests possible causes.

Blood and urine tests may detect a disorder that is causing polyneuropathy, such as diabetes, kidney failure, or an underactive thyroid gland.

Infrequently, a nerve biopsy is necessary.

Sometimes polyneuropathy affecting the hands and feet is the first indication that people have diabetes. Sometimes, when extensive testing detects no obvious cause, the cause is a hereditary neuropathy that affects other family members so mildly that the disorder was never suspected.

If weakness is widespread and rapidly worsening, doctors do other tests:

A spinal tap (lumbar puncture) is done to obtain a sample of cerebrospinal fluid, which surrounds the brain and spinal cord. If the protein level in the fluid is high and few or no white blood cells are present, the cause may be Guillain-Barré syndrome.

Spirometry is done to determine whether the muscles that control breathing are affected. Spirometry is used to measure how much air the lungs can hold as well as how much and how quickly air can be exhaled.

Treatment of Polyneuropathy

Treatment of the cause

Relief of pain

Sometimes physical and occupational therapy

Specific treatment of polyneuropathy depends on the cause, as for the following:

Diabetes: Careful control of blood sugar levels may slow progression of the disorder and occasionally relieves symptoms. Transplantation of cells that produce insulin (islet cells—see Pancreas Transplantation), located in the pancreas, is sometimes done and may result in a cure.

Autoimmune disorders: Treatments include plasma exchange (filtering of toxic substances, including abnormal antibodies, from the blood), immune globulin (a solution containing many different antibodies collected from a group of donors) given intravenously, corticosteroids, and drugs that inhibit the immune system (immunosuppressants).

Drugs and toxins: Stopping the drug or avoiding exposure to the toxin can sometimes reverse the polyneuropathy. Antidotes are available for certain drugs and toxins and can reverse some toxic effects.

Excessive amounts of vitamin B6: If the vitamin is stopped, polyneuropathy may resolve.

Some drugs that are usually not considered pain relievers can lessen pain due to nerve damage. They include the antidepressant amitriptyline, the anticonvulsants gabapentin and pregabalin, and mexiletine (used to treat abnormal heart rhythms). Lidocaine, an anesthetic applied as a lotion, an ointment, or a skin patch, may also help.

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